Sputtering target, method of making same, and high-melting metal powder material

ABSTRACT

There is provided a method of making a high-melting metal powder which has high purity and excellent formability and, particularly, of a metal powder of spherical particles made of Ta, Ru, etc. having a higher melting point than iron. There is also provided a target of high-melting metal or its alloy, which is made by the sintering under pressure of these powders and which has high purity and a low oxygen concentration and shows high density and a fine and uniform structure. A powder metal material mainly composed of a high-melting metal material is introduced into a thermal plasma into which hydrogen gas has been introduced, thereby to accomplish refining and spheroidizing. Further, an obtained powder is pressed under pressure by hot isostatic pressing, etc.

CROSS REFERENCE TO RELATED APPLICATIONS

This is a continuation of application Ser. No. 09/612,561 filed Jul. 7,2001, the disclosure of which is incorporated herein by reference.

BACKGROUND OF THE INVENTION

The present invention relates to a sputtering target comprising arefractory metal material, such as Ta and Ru, particularly for use inthe manufacture of semiconductor LSIs and a method of making thesputtering target.

Conventionally, Al and Al alloys have been used as wiring materials forsemiconductor LSIs. However, with the recent high integration design,minute design and high-speed design of operation of LSIs, it has beenexamined to use Cu which has higher electromigration (EM) resistance andhigher stress migration (SM) resistance and provides low electricresistance. However, Cu readily diffuses into the SiO₂ of interlayerdielectric film and also into an Si substrate and, therefore, it isnecessary to enclose Cu wiring with a diffusion barrier layer. As thebarrier materials for Cu, a TaN film formed by performing reactivesputtering in an atmosphere of argon and nitrogen through the use of aTa sputtering target and a Ta—X—N film formed by performing reactivesputtering through the use of a Ta—X alloy target are considered good.For this reason, Ta and Ta—X alloy sputtering targets for barrier metalapplication for semiconductor LSIs have been developed.

On the other hand, in a DRAM and FeRAM of semiconductor memory, a Ptfilm formed by the sputtering of a Pt target has so far been used as acapacitor electrode. However, with further large capacity design, it isbeing examined to use an Ru film formed by performing the sputtering ofan Ru target as a capacitor electrode.

In the manufacture of targets of the above high-melting metals or theiralloys (Ta, Ta alloys, Ru, etc.), any one of a melting-plastic workingprocess and a powder sintering process can be selected, while the powdersintering process is most suited. Reasons for this are described below.

First, although the hot plastic working of Ta is possible, it is verydifficult to make crystal grains uniform and fine. According to resultsof an investigation performed by the present inventors, coarsenedcrystal grains of a target are one of the major causes of generation ofparticles during sputtering. Recently, addition of a third alloyingelement to Ta—N has been proposed in order to improve the barrierproperty of a Ta—N film. Si and B are mentioned as such alloyingelements and it is said that a Ta—X—N film formed by the reactivesputtering of a Ta—X target (X: alloying element such as Si and B)becomes amorphous, thereby improving the barrier property. However, aTa—X alloy target raises a problem that plastic working is impossibledue to the segregation by solidification and the formation ofintermetallic compounds.

On the other hand, in the case of Ru, manufacture by plastic working isimpossible because this metal does not have plastic workability.Therefore, it can be said that the superiority of the powder sinteringprocess, including an advantage of yield improvement in thenear-net-shape manufacture of targets, is clear as a method of makinghigh-melting metal targets of Ta, Ta—X alloys and Ru.

Incidentally, with the recent high integration design of LSIs and minutedesign of devices, requirements for a reduction of impurities inmaterials for thin films have become very severe. In particular, fortransition metals (Fe, Ni, Cr, etc.) and alkali metals (Na, K, etc.)which are considered to have a great adverse effect on the performanceof devices, it is required to reduce such impurities to the order ofppb, and for radioactive elements (Th, U, etc.) to the order of ppt.Furthermore, for other low-melting metal impurities also, it is requiredto lower their concentrations and, as a result, it is necessary toincrease purity to not less than 99.999%. In addition, in order toimprove the thermal stability of barrier films, the interface electriccharacteristic of DRAM capacitor electrode films, etc., it is alsorequired to lower oxygen concentrations to not more than 100 ppm.

Ta powders that can be industrially supplied are conventionally obtainedby an ingot crushing process after performing the EB melting of alow-purity Ta raw material, and their purity is only a level of 4N atthe most. On the other hand, the following method, for example, isadopted as a process for industrially making Ru. Caustic potash andpotassium nitrate are added to crude Ru, thereby converting Ru intosoluble potassium ruthenate. This salt is extracted in water and isheated during chlorine gas injection under the formation of RuO₄, whichis then collected in dilute hydrochloric acid containing methyl alcohol.This liquid is evaporated and dried, and is then calcined in an oxygenatmosphere to form RuO₂, with the result that Ru metal is finallyobtained by reduction under heating in hydrogen. Commercial Ru powdersmade by this method contained low-melting metal impurities, alkalimetals, and residues of halogen elements such as Cl and hence could notmeet the purity required of capacitor electrode films. Moreover, powdersmade by this method were coral-like porous agglomerates and had very lowpacking densities in the case of sintering.

In order to increase the purity of Ta and Ru targets, there have beenproposed methods of refining the above raw material by EB melting, moreconcretely, a method which involves plastic working of an Ta ingotobtained by the EB melting and a method of machining an Ru ingotobtained by the EB melting into a target in a casting condition thereof.For example, JP-A-3-197940 discloses a method of plastically working anTa ingot obtained by EB-melting. Also, JP-A-6-264232 discloses a methodof performing plastic working and heat treatment of Ta after the EBmelting thereof. Further, JP-A-11-61392 discloses a method of machiningan ingot obtained by the EB melting of an Ru raw material and using itin a casting condition thereof.

High purity may be realized by using the methods disclosed in the aboveliterature. In those cases, however, as mentioned above, there is a fearof causing a coarse or nonuniform of the microstructure at the stage ofplastic working of an ingot. Further, with a material in a castingcondition, the presence of a large number of pores and casting defectscannot be neglected. In addition, in the melting methods, it isimpossible to perform near-net-shape forming and the yield of noblemetals is low. In other words, it can be said that the melting methodsproposed in the above literature are an unavoidable choice because highpurity and low oxygen concentrations could not be realized in the powdersintering method.

In general, it is difficult to sinter the refractory metals (moreconcretely, metals each having a melting point higher than that of iron)to high density in order to increase the density of a sintered compact,pressure sintering is one of effective methods. Because metal powdersare filled into a capsule and then the capsule with packing powders issintered, the packing condition of a raw material powder is an importantfactor. In hot isostatic press (HIP), increasing the packing densityaccelerates an increase in the density of a sintered compact and reducesabnormal shrinkage during sintering and sinter cracks, resulting in anincrease in yield. In other words, in performing sintering underpressure, packing a raw material powder at a high density and uniformpacking bear an important meaning. It is well known that thespheroidizing treatment of a raw material powder is effective inrealizing such high packing density and uniform packing. However, incase of using a crushed Ta powder and a coral-like Ta powder, thepacking density is low and, therefore, the optimization (spheroidizing)of these powder shapes is also an important problem in the sinteringtechnology of targets.

As a method for realizing the spheroidizing of a high-melting metalpowder, JP-A-3-173704 discloses a method of producing a spherical Tapowder by Plasma Rotating Electrode Process (PREP) treatment, i.e., bybringing a thermal plasma into contact with a rotating electrode andthereby causing an electrode material to melt and splash. Under thismethod, however, the thermal plasma is given with the purpose of onlyspheroidizing performed by heating and melting, and the effect ofpurification of powder cannot be expected.

SUMMARY OF THE INVENTION

Therefore, an object of the invention is to provide a method of making ahigh-melting metal powder which has high purity and which is excellentin compacting and sintering, and particularly a method of making aspherical powder made of Ta, Ru, etc. having a higher melting point thanthat of iron. Another object of the invention is to provide a targetmade of high-melting metals or its alloy, which is producted bysintering these powders under pressure and which has high purity and lowoxygen concentrations and besides shows high density and a fine anduniform micro-structure.

In order to attain the above objects, the present inventors haveconducted research energetically and found out that by applying thermalplasma treatment to a raw material powder, it is possible to spheroidizea high-melting metal powder and, at the same time, to obtain high purityand low oxygen concentrations. Further, the inventors have found outthat by performing sintering under pressure through the use of thispowder which is spherical and has high purity and a low oxygenconcentration, it is possible to increase packing density, with theresult that it is possible to obtain a sintered powder compact suitablefor sputtering targets, which has high purity and a low oxygenconcentration and besides shows a high density and a uniform and finemicro-structure.

In the method of making a target according to the invention, byintroducing a powder mainly composed of a high-melting metal into athermal plasma flame, refining and spheroidizing are performed and anobtained powder is sintered under pressure. As a result of this process,it is possible to obtain a sputtering target which has high purity and alow oxygen concentration and besides shows high density and a uniformand fine micro-structure.

Further, in the method of making a target according to the invention, apowder is introduced into a thermal plasma into which hydrogen gas hasbeen introduced. As a result of this process, it is possible to obtain asputtering target having chemical composition which has high purity anda low oxygen concentration and besides shows high density and a uniformand fine micro-structure.

Also, in the method of making a target according to the invention, thesintering under pressure is hot isostatic pressing. As a result of thisprocess, it is possible to obtain a sputtering target which shows highdensity and a uniform and fine micro-structure.

The sputtering target according to the invention comprises a sinteredpowder compact with a relative density of not less than 99%, a purity ofnot less than 99.999% and an oxygen concentration of not more than 100ppm. As a result of this matter, a thin film obtained by sputteringthrough the use of this target has high purity and is uniform so as toimprove the reliability of products.

Also, the sputtering target according to the invention is obtained byperforming the sintering under pressure of a powder obtained byintroducing a powder material mainly composed of a high-melting metalinto a thermal plasma. As a result of this process, a thin film obtainedby performing sputtering through the use of this target has high purityand is uniform, improving the reliability of products.

Also, the sputtering target according to the invention is obtained byintroducing a powder into a thermal plasma into which hydrogen gas hasbeen introduced. As a result of this, a thin film obtained by performingsputtering through the use of this target has high purity and is uniformso as to improve the reliability of products.

Also, in the sputtering target according to the invention, the shape ofparticles of the powder introduced for sintering under pressure isspherical or analogous to a sphere. As a result of this, the targetshows high density and a uniform and fine micro-structure, and theuniformity of a thin film obtained by performing sputtering through theuse of this target increases.

Further, in the sputtering target according to the invention, the abovehigh-melting metal material is Ta. As a result of this matter, it ispossible to obtain a Ta target which has high purity and a low oxygenconcentration and shows high density and a uniform and finemicro-structure, and by using this Ta target, it is possible to obtain aTa thin film which has high purity and is uniform.

Further, in the sputtering target according to the invention, the abovehigh-melting metal is Ru. As a result of this matter, it is possible toobtain an Ru target which has high purity and a low oxygen concentrationand shows high density and a uniform and fine micro-structure, and byusing this Ru target, it is possible to obtain an Ru thin film which hashigh purity and is uniform.

Further, the high-melting metal powder according to the invention has apurity of not less than 99.999% and an oxygen concentration of not morethan 100 ppm and the shape of particles of the high-melting metal powderis spherical or analogous to a sphere. By performing pressure sinteringwith the use of this powder, the packing density of the powder increasesand it is possible to obtain a formed powder compact which shows highdensity and a uniform and fine micro-structure.

Further, the high-melting metal powder material according to theinvention is obtained by introducing a powder mainly composed of ahigh-melting metal into a thermal plasma. As a result of this process,the obtained high-melting metal powder becomes a powder of sphericalparticles which has high purity and a low oxygen concentration as achemical composition, and by performing pressure sintering through theuse of this powder, it is possible to obtain a formed powder compactwhich has high purity and a low oxygen concentration and besides showshigh density and a uniform and fine micro-structure.

Further, the high-melting metal powder according to the invention isobtained by introducing a powder into a thermal plasma into whichhydrogen gas has been introduced. As a result of this process, theobtained high-melting metal powder material becomes a powder ofspherical particles which has high purity and a low oxygenconcentration, and by performing pressure forming through the use ofthis powder, it is possible to obtain a formed powder compact which hashigh purity and a low oxygen concentration and besides shows highdensity and a uniform and fine micro-structure.

As mentioned above, the greatest feature of the invention resides in thefact that a powder mainly composed of a metallic material with a highermelting point than iron, particularly Ta or Ru, is introduced into athermal plasma, thereby to obtain a high-melting metal powder materialwhich has high purity and a low oxygen concentration and the shape ofwhose particles is spherical or analogous to a sphere. When aradio-frequency (RF) thermal plasma is specifically selected from amongthermal plasmas and used as a heat source, the range of the thermalplasma widens and it is possible to suppress the contact of the powderwith other substances during treatment. This is most favorable forobtaining high purity.

Further, by introducing hydrogen into a thermal plasma gas, it ispossible to remarkably improve the evaporation of impurities and theeffect of the reduction of oxygen owing to the generation of ions andexcited atoms of hydrogen.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a schematic view of the structure of a thermal plasmatreatment apparatus used in the invention.

FIGS. 2A and 2B are micrographs obtained by a scanning electronmicroscope for showing changes in the shape of Ta powder particlesbefore and after the thermal plasma treatment.

FIGS. 3A and 3B are micrographs obtained by a scanning electronmicroscope for showing changes in the shape of Ru powder particlesbefore and after the thermal plasma treatment.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

Embodiments of the invention will be described below. With reference toan apparatus shown in FIG. 1, a procedure for performing the thermalplasma treatment of a powder will be explained through the use of theabove thermal plasma treatment apparatus for powder treatment.

1. A raw material powder (110) is charged into an electro-magneticpowder feeder (hereinafter referred to simply as a powder feeder) and athermal plasma generator comprising a thermal plasma torch (not shown inthe figure) and a chamber (106) is evacuated to a vacuum of up to 10−3Pa.

3. The raw material powder (110) is introduced by transportation on acarrier gas from the powder feeder (101) via a nozzle (102) into theplasma high-temperature zone (105) having a temperature between 5,000 to10,000° K. At this time, the raw material powder (110) is melted andbecomes spherical due to the action of the surface tension of the liquidphase of the metal.

5. After the completion of the treatment, the plasma gas (120) and powersource are stopped and powder after the treatment is recovered from apowder recovery can (108). It is possible to perform the recovery bothin a protective gas and in the air.

In the thermal plasma high-temperature zone (102), the raw materialpowder (110) is melted and becomes spherical due to the action of thesurface tension of the metal, and as a result of this process, the shapeof the powder particles after the treatment becomes spherical.

Further, oxides and low-melting impurities contained in the raw materialpowder (110) evaporate in the thermal plasma high-temperature zone (105)because their vapor pressures are higher than those of Ta and Ru. As aresult of this condition, the purity of the raw material powder (110)increases and, at the same time, its oxygen concentration decreases.However, the pressure of the plasma gas used here is almost atmosphericpressure and hence the effect of the evaporation of impurities is notgreat with an argon thermal plasma treatment alone. In such cases, ifhydrogen is introduced thereinto, it is possible to further lower theoxygen concentration by the reduction reaction of hydrogen ions, excitedatoms, etc. In the invention also, the introduction of hydrogen gasenables the effect of the evaporation of impurities to be remarkablyimproved.

Hot pressing or hot isostatic pressing (HIP) is performed through theuse of a high-melting metal powder obtained in the manner shown above.In HIP, in particular, a powder is packed in a capsule made of carbonsteel on the bottom of which a piece of Mo foil is laid, and HIP isperformed after deaeration and sealing in a vacuum. It is desirable thatthis powder be sintered under pressure at a temperature of not less than1100° C. and at a pressure of not less than 50 MPa. Next, the abovesintered powder compact is subjected to machining or surface grindingand is bonded to a packing plate, thereby to complete a target.

In conventional powders, the shrinkage during sintering was greatbecause of their low packing densities and it was necessary to considerextra thicknesses and diameters in order to ensure target sizes. Inaddition, yields were low because of abnormal shrinkage and sinteringcracks. It has become apparent that, in contrast to this matter, byimproving packing density through the use of a powder of sphericalparticles obtained with the aid of a thermal plasma as mentioned above,for example, in a case where a target with a size of 350 to 400 mm indiameter×10 mm in thickness is to be made, it is possible to reducepowder consumption by 10 to 30% in comparison with conventional powders.

EXAMPLE 1

Examples of the invention will be explained below. The treatment of Tapowders was actually carried out through the use of an apparatus of thestructure shown in FIG. 1. The Ta raw material powders used in thetreatment and thermal plasma treatment conditions are shown in Table 1.Further, with respect to changes in the shape of powder particles beforeand after the thermal plasma treatment, micrographs of Specimen 3, as anexample, obtained by a scanning electron microscope are shown in FIGS.2A and 2B. FIG. 2A is a photograph of a raw material powder (before thethermal plasma treatment) and FIG. 2B is a photograph of Specimen 3(after thermal plasma treatment).

Next, the powder after the thermal plasma treatment was packed in an HIPcan and the packing density at that time was measured. The result of themeasurement is shown in Table 1. Further, a Ta target with a size of 350mm in diameter×10 mm in thickness was fabricated from the powder ofspherical particles under the sintering conditions of 1350° C.−155 MPa−1hour. The packing density was measured, and the result of themeasurement is also shown in Table 1.

Further, an impurity analysis of the sintered Ta compact was made withthe aid of a GD-MS (glow discharge-mass spectrometer). The result of theanalysis is shown in Table 2. Incidentally, in order to make clear theeffects of the thermal plasma treatment on the packing density andchemical composition of the sintered powder compact, the samemeasurements as mentioned above were carried out also for the rawmaterial powder not subjected to the thermal plasma treatment, and theresults of these measurements are also shown in Tables 1 and 2.

The results of the above examination will be looked over. First, it isapparent from Table 1 that each of Specimens 1 to 3 subjected to thethermal plasma treatment, has a packing density of not less than 60% inan HIP can and a sintering density of almost 100%, both showing asubstantial increase in comparison with the raw material powder that isa comparative example. This is because, as shown in FIGS. 2A and 2B, theshape of powder particles became spherical due to the thermal plasmatreatment.

As made clear from the result shown in Table 2, the purity of Ta isincreased from a level of 3N to levels of 4N and 5N by the thermalplasma treatment. From the foregoing it has become apparent that a Tatarget obtained from a Ta powder subjected to the thermal plasmatreatment by pressure sintering is most suited to the formation of a TaNfilm by reactive sputtering.

EXAMPLE 2

Chemically processed powder Ru was examined in the same manner as withExample 1. The Ru raw material powders and thermal plasma treatmentconditions as well as measurement results of HIP can packing density andsintering density are shown in Table 3. Further, with respect to changesin the shape of powder particles before and after the thermal plasmatreatment, micrographs of Specimen 6, as an example, obtained by ascanning electron microscope are shown in FIGS. 3A and 3B. FIG. 3A is aphotograph of a raw material powder (before the thermal plasmatreatment) and FIG. 3B is a photograph of Specimen 6 (after thermalplasma treatment). Further, an Ru target with a size of 400 mm indiameter×10 mm in thickness was fabricated from the powder of sphericalparticles. An impurity analysis of the Ru target after sintering wasmade, and the result of the analysis is shown in Table 4.

From the results shown in Table 3, it is apparent that each of Specimens4 to 6 subjected to the thermal plasma treatment, has an HIP can packingdensity of not less than 60% and a sintering density of almost 100%,both showing a substantial increase in comparison with the raw materialpowder that is a comparative example. This is because, as shown in FIGS.3A and 3B, the shape of powder particles became spherical due to thethermal plasma treatment.

From the result shown in Table 4, it is apparent that the purity of Ruis increased from a level of 3N to levels of 4N and 5N by the thermalplasma treatment. From the foregoing it has become apparent that an Rutarget obtained from an Ru powder subjected to the thermal plasmatreatment by pressure sintering is most suited to the formation of an Rufilm by sputtering.

TABLE 1 Compara- tive example (Raw material Specimen Specimen Specimenpowder) 1 2 3 Plasma Particle 250-325 250-325 325-425 250-325 treat-size of raw meshes meshes meshes meshes ment material condi- powdertions Plasma — 45 kW 28 kW 40 kW power Composition — Ar Ar + 8% Ar + 30%of plasma H₂ H₂ gas Flow rate — 80 75 85 of plasma gas (l/min) Flow rate— 10 10 15 of carrier gas (l/min) Sinter- HIP can 46.8 62.5 63.1 82.7ing packing density Sintering 96.3 99.6 99.8 99.9 density

TABLE 2 Comparative example (Raw material Specimen Specimen Specimenpowder) 1 2 3 Na 0.785 0.681 0.008 <0.001 Mg 0.624 0.411 0.027 0.018 Al3.761 2.522 0.201 0.146 Si 10.192 7.804 0.603 0.410 P 0.220 0.321 0.2270.255 S 0.591 0.580 0.041 0.034 Cl 2.572 0.726 0.010 0.005 K 3.871 1.0730.027 0.001 Ca 1.442 0.516 0.013 0.007 Ti 4.433 4.162 0.357 0.041 V0.020 0.021 <0.007 <0.004 Cr 13.644 11.956 0.976 0.759 Mn 0.932 1.0330.352 0.366 Fe 38.431 37.523 0.970 0.178 Co 0.827 0.786 0.034 0.026 Ni4.700 3.384 0.803 0.715 Cu 6.812 4.920 0.621 0.490 Nb 0.559 0.587 0.5120.523 Mo 4.037 4.121 1.136 0.980 Ru 0.152 0.171 0.144 0.130 Pb 0.1790.195 0.083 0.067 In 0.251 0.264 0.141 0.102 Ir 0.053 0.071 0.059 0.056Th 14.930 3.726 27.417 20.307 ppb ppb ppt ppt U 19.465 16.357 53.06041.150 ppb ppb ppt ppt C 23.716 <20 <10 <10 N 1.504 1.316 0.882 0.627 O1450 1410 96 38 Purity of 99.98% >99.99% >99.999% >99.999% Ta Note: Unitof impurity element concentration: (ppm) Purity of Ta: Purity excludinggas portion (%)

TABLE 3 Compara- tive example (Raw material Specimen Specimen Specimenpowder) 4 5 6 Plasma Particle 200-325 100-250 200-325 200-325 treat-size of raw meshes meshes meshes meshes ment material condi- powdertions Plasma — 45 kW 28 kW 40 kW power Composition — Ar Ar + 8% Ar + 30%of plasma H₂ H₂ gas Flow rate of plasma — 80 75 85 gas (l/min) Flow rateof carrier — 10 10 15 gas (l/min) Sinter- HIP can ing packing 33.3 65.266.2 65.8 density Sintering 96.7 99.7 99.9 99.9 density

TABLE 4 Comparative example (Raw material Specimen Specimen Specimenpowder) 4 5 6 Na 2.383 1.904 0.117 0.024 Mg 2.300 1.832 0.213 0.078 Al5.837 4.983 0.640 0.182 Si 3.409 2.114 0.175 0.100 P 0.644 0.563 0.2720.061 S 0.121 0.101 0.041 0.080 Cl 61.504 6.033 0.780 0.064 K 4.3701.754 0.061 0.004 Ca 1.363 0.712 0.032 0.002 Ti 1.156 0.982 0.084 0.040V 0.121 0.118 0.087 0.074 Cr 0.504 0.511 0.027 0.018 Mn 0.123 0.1120.063 0.044 Fe 6.548 5.861 0.143 0.110 Co 1.278 1.004 0.254 0.107 Ni2.693 1.508 0.621 0.087 Cu 2.771 1.019 0.276 0.061 Nb 0.034 0.045 0.0420.041 Zr 0.787 0.658 0.094 0.035 Mo 0.071 0.067 0.078 0.070 Rh 0.3040.401 0.417 0.409 In 2.804 2.201 0.409 0.006 Sn 3.565 1.870 0.186 0.207Sb 2.380 1.306 0.122 0.098 Ta 0.227 0.229 0.374 0.391 W 0.102 0.1100.131 0.137 Th 77.234 73.701 <0.010 <0.010 ppt ppt ppt ppt U 385.720250.144 <98.289 <71.143 ppt ppt ppt ppt C <2 <2 <2 <12 N <0.2 <0.2 <0.2-<0.2 O 1278 87 21 <10 Purity of 99.95% >99.99% >99.999% >99.999% RuNote: Unit of impurity element concentration: (ppm) Purity of Ru: Purityexcluding gas portion (%)

As mentioned above, according to the invention, by performing thethermal plasma treatment through the use of a thermal plasma into whichhydrogen is introduced, an increase in purity, a decrease in oxygenconcentration, and the spheroidizing of high-melting metal powdermaterials of Ta, Ru, etc. can be simultaneously realized. Furthermore,by performing the sintering under pressure of an obtained powder, it ispossible to realize a Ta or Ru target which shows high density and afine and uniform micro-structure and which has high purity and a lowoxygen concentration and to obtain an optimum sputtered thin film.

What is claimed is:
 1. A method of refining a metal powder comprisingthe steps of: passing a metal into a thermal plasma into whicha-hydrogen gas is introduced; and refining the metal powder to have apurity of not less than 99.999% and an oxygen concentration of not morethan 100 ppm.
 2. A method of refining a metal powder according to claim1, comprising passing the metal powder into a thermal plasma into whichhydrogen gas is introduced, wherein the metal powder has a purity of notless than 99.9%.
 3. A method of making a target comprising the steps ofintroducing a metal powder mainly composed of refractory metal into athermal plasma into which hydrogen gas has been introduced, thereby toperform simultaneous refining of the metal powder and spheroidizing ofthe metal powder; and sintering the obtained metal powder underpressure.
 4. A method of making a target according to claim 3 comprisingthe steps of introducing the metal powder mainly composed of refractorymetal into the thermal plasma into which hydrogen gas has beenintroduced, thereby to perform simultaneous refining of the metal powderand spheroidizing of the metal powder; and sintering the obtained metalpowder under hot isostatic pressing.
 5. A method of making a targetaccording to claim 3, comprising the steps of introducing the metalpowder mainly composed of refractory metal into the thermal plasma intowhich hydrogen gas has been introduced, thereby to perform refining ofthe metal powder to a purity of not less than 99.99% and an oxygenconcentration of not more than 100 ppm.
 6. A method of making a targetaccording to claim 3, comprising the steps of introducing the metalpowder mainly composed of refractory metal into the thermal plasma intowhich hydrogen gas has been introduced, thereby to perform refining ofthe metal powder to a purity of not less than 99.999% and an oxygenconcentration of not more than 100 ppm.
 7. A method of making a targetaccording to claim 3, comprising the steps of introducing the metalpowder having a purity of not less than 99.9% mainly composed of therefractory metal into the thermal plasma into which the hydrogen gas hasbeen introduced.